1. Field of the Invention
The present invention relates to call set-up and service invocation in telecommunications networks, in particular to Intelligent Networks (IN)-based mobile telecommunications networks.
2. Description of Related Art
There is currently considerable activity in international standards bodies (CCITT, ISO, etc.) and elsewhere in developing Intelligent Network standards and implementations. Put simply, the basis of an intelligent network is to separate service provision from switching functionality in telecommunications networks. Typically, the processing required to implement network services is provided by processors which are physically and logically separate from the switching infrastructure and control it. This allows for rapid creation and introduction of new services without their design or implementation being excessively constrained by the characteristics of the network switches. In particular, a service may be provided throughout a network without the need to modify every individual network switch.
In present day IN standards (CCITT Capability Set 1 (CS1) and implementations the logical platform for launching all IN services is a xe2x80x9cBasic Call State Modelxe2x80x9d (BCSM) modelled in the software of each IN switch in a network. The BCSM defines a finite number of states in the lifetime of a telecommunication call, e.g. off-hook, collect digits, etc. Within the BCSM a number of Detection Points (DPs) are identified, at which certain events can trigger a switch to suspend its call processing and refer to service control entities for further instructions and service-request processing. The service control entity can then control the switch to allow it to continue, terminate or modify its call processing according to the service requested.
Service control entities are able to modify the call processing by performing further processing. For example:
a) Performing checks upon the validity and account details of the calling user""s identity;
b) Obtaining further information to aid call completion: this may include obtaining the routing number, comparing service requests for compatibility, and checking the called party""s status, e.g. whether already engaged on another call, and whether diversion or a mailbox facility is available.
If a service control entity determines from these further processing steps that a call is to be made, it then returns control of the call to the switch and the call set-up continues with routing, alerting and answer. The elements of the call set-up procedure may have been modified by the service control entity, e.g. if a call diversion is in operation for the called number, or differentiated ringing tones are in use by the called party for different calling numbers. All service and call requests are initially handled by the switch, the operation of the service control entity being determined by the current status of the switch""s BCSM.
Intelligent Networks have great potential for offering advanced network services in the future. It has been proposed to use these principles as the basis for future mobile telecommunication systems (as well as fixed systems) and while a number of enhancements needed to achieve this have already been identified, further changes will be required. A number of systems have been developed to make use of IN principles to provide more efficient call connections and other, non-call, services. In particular, reference is made to Patent Specifications WO93/16543 (Ericsson), and U.S. Pat. No. 4,910,766 (Ogino), and Giridharagopal: xe2x80x9cIntelligent Networks; Demands on Provisioning and Performancexe2x80x9d: Proceedings of the 12th InternationalTeletraffic Congress, No 1, 1989 (Amsterdam), pages 447 to 454. The systems described in these documents all route service requests, by way of a local switch, to a xe2x80x9cService Control Centrexe2x80x9d which then controls further trunk switching, or other services.
A generalised description of these current techniques of intelligent network call set-up is illustrated schematically in FIGS. 1a and 1b. As shown in FIG. 1a the logical interconnection of the schematically illustrated telecommunications network is as follows: a terminal 1 is connected to a switch 2 by a communications link 4, and the switch 2 is connected to a service control unit 3 by means of a control link 6, and to other terminals 8, by means of a communications link 5, either directly or through other switches. The logical communications links 4, 5 are carried over physical links, which may be permanent (wired) links to fixed terminals or may be dynamically variable links having no permanent physical existence except when required to form a communications connection, for example the radio links in a mobile radio network, or the links in the fixed trunk network (in which the individual physical links are only allocated to individual end-to-end calls for the duration of those calls).
FIG. 1b shows a flow diagram for the operation of the system of FIG. 1a. A call or other service request is directed by a user from the terminal 1 to the switch 2 (step 21), over the communications link 4. If a call request is made requiring further processing, the switch recognises this and switch processing is interrupted (step 22). The switch 2 then directs such a request for further processing of the call to the service control unit 3 (step 23), by way of the control link 6. The service control unit 3 provides the checking and further computation required to create instructions for the switch 2 to complete the call request or to perform some other service request (step 24). In the case of a call request, the service control unit 3 then returns the required instructions to the switch (step 25) to enable the call to be routed and completed (step 27), by allocating a further communications link 5 in order to complete the communications connection. In practice there will be several interconnected switches 2, each serving a number of terminals 1, and each having access to one or more service control units 3 providing different services. The remote terminal 8 is then alerted to the call and responds (step 28).
On initiation of a request for a call or other transaction (e.g. a service request) a communications connection, capable of carrying both signalling and call traffic, is established using the communications link 4 between the terminal 1 and the switch 2. Resources in the switch 2 are then dedicated to completion of the connection required. However, the resources may not be required if the service processing step 24 determines that the communications connection 5 to the remote terminal 8 is not to be completed. When the switch 2 requests processing from the service control unit 3, the service control unit 3 may fail the call and cause the switch 2 to release the connection link 4 due to a service mismatch, customer specific service (such as outgoing calls barred) or called party terminal state (such as the busy condition). This will mean that, in addition to a signalling channel, a traffic channel will have been connected on the communications link 4 from the user terminal 1 to the switch 2 and in the switch 2 itself, and then not used. For a mobile telecommunications system, such as a cellular radio system, this is of significance because the communications link 4 is not permanently allocated to the terminal 1 as it would be in a fixed system. Instead, a radio channel is only allocated when a terminal 1 requires it. Whilst allocated to one call attempt, these resources cannot be used by other call attempts, which may then fail for lack of available capacity.
According to a first aspect of the invention there is provided a switched mobile telecommunications network for providing communications connections between mobile network terminations and other network terminations, the network comprising:
one or more mobile network terminations;
service processing means for providing services to or for the mobile network terminations;
the service processing means being initially accessible by service requests from the mobile network terminations by signalling connections, without establishment of a communications connection with the mobile network termination;
and switching means controllable by the service processing means in order to establish a communications connection with the originating mobile network terminal only if required by the service requested by the mobile network termination.
(It should be noted that the xe2x80x9cotherxe2x80x9d network terminations referred to above may include both mobile and fixed network terminations).
This invention enables a mobile user terminal to direct service requests (including call set-up requests) directly to the service processing means, the switch not being involved with the call or service request unless the service processing means then instructs it to participate. Instructions such as call connection may require use of the switch capability, but other, non-call-related instructions, such as setting up a call divert service, will not do so. Certain other functions, such as accessing a voice mail box, may require a communications connection only between the network termination and a component independent of the main switching function. This invention effectively migrates call and service control functionality from the switch into the service processing means, with the switch""s functionality being reduced to a basic switch xe2x80x98matrixxe2x80x99. Because, in a mobile telecommunications system, the links between mobile terminals and switches are not permanently dedicated to individual terminals, the invention also allows the establishment and allocation of resources to be deferred until it is clear that such resources are required.
According to a second aspect of the invention, there is provided a method of operating a switched mobile telecommunications network, the method being such that all service requests are initially directed from their originating network terminations by establishing a signalling connection to a service processing means, without establishment of a communications connection with the mobile network termination, and the service processing means provides services to the network termination over the signalling connections, the service processing means also controlling switching means to establish a communications connection with the respective network termination only if required by the service requested.
In this specification the term xe2x80x9cservice requestxe2x80x9d embraces a request from a mobile network termination to establish a communications connection with a second network termination. When the service request is such a request, the service request is directed to the service processing means which controls switching means to establish the required communications connection. The second network termination to which the mobile network termination is connected need not necessarily be the one requested. For example, the user of the requested second termination may have diverted incoming calls to another termination.
When a request from a mobile network termination to establish a service not requiring a communications connection (i.e. only a signalling connection) is directed to the service processing means, the service processing means will provide the service without establishing a full communications connection to the network termination. The service processing means may transmit a control message to the mobile network termination.
In one arrangement the service processing means, on receiving an executable call request from a first mobile network termination, establishes a communication connection through a switching means between the first network termination and a second network termination, and on receiving a non-call service request or a non-executable call request establishes a communication connection with a network service termination.